Screw-shell contact for electrical sockets



Sept. l 7, l 929.

E. K. FREEMAN SCREW SHELL CONTACT FOR ELECTRICAL SOCKETS Filed March 22, 1927 Patented Sept. 17, 1929,:

. UNITED STATES PATENT OFFICE EDGAR KENNETH FREEMAN, or TRENToN, NEW JERSEY, AssIeNoR To CIRCLE 1r.

MEG. co., E TREN'roN, NEW JERSEY, A CORPORATION 0E NEW JERSEY SCREW-SHELL CONTACT FOR ELECTRICAL SOCKETS l Application led March 22, 1927. Serial No. 177,350.

This invention relates to electrical lamp 'sockets or receptacles, and more particularly toylnovel and practical means for ripping the plug of the lamp so that it wi not be 5 accidentally displaced.

To that end the invention contemplates a simple and practical screw shell construction which uniformly grips the plug of the lamp over its entirecontacting surface, thereby affording added security against accidental displacement and yet at the same time permitting of the plug of the lamp being easily inserted and removed when desired. While various expedients have been heretofore resorted to for gripping the plug of the lamp,

nevertheless where the gripping ,means utilized the screw shell contact as a part of such means, it has been customary to grip'the lamp in a restricted zone or at one point only. Also in some constructions employing a spring for holding the lamp base inthe screw shell, a depression or indentation is made in the lamp base and this frequently proves to be a detriment since it makes it diiiicult to remove the plug. With the present construction and arrangement however, these objections are overcome. p

A further object of the invention is to provide a construction which may be easily manufactured and assembled` and which is inexpensive to make and reliable in use.

With the above and other objects in view which will more readily appear as the nature of the invention is better understood, the same consists in the novel construction, combination and arrangement of 'parts hereinafter more fully described, illustrated and claimed.

A preferred embodimentof the invention 40 is shown in the accompanying drawings, in'

which Fig. 1 is a view of an electrical receptacle, partly in section, illustrating the present iinprovements.

Fig. 2 is a bottom plan view of the receptacle shown in Fig. 1. v

Fig. 3 is an enlarged detail sectional View taken on the line 3-3 of Fig. l. a lamp plug being shown in the screw shell member.

Fig. 4 is a detail perspective view of the holding unit which includes the screw and tensioning spring.

Similar reference characters designate corresponding parts throughout the several figures of the drawings.

In carrying the present invention into effectit is particularly desired to avoid a construction wherein catches, pawls or other relatively fragile parts are used for maintaining a friction grip on the screw-threaded base or lamp plug. In other Words, the invention aims to utilize the screw shell contact in such a Way that the lamp plug or base may be screwed in for use in the usual way without obstruction or interference, and without contacting or engaging with anything but the screw shell contact itself until itreaches the usual center-plug contact.

Accordingly, as will be observed from the drawings it is proposed to utilize a screw shell designated generally as S havin the flanges 1 at one end for connecting wit the porceshell lain body B in the usual manner, and also having the opening 2 providing the necessary clearance for the center plug contact 3 of the rece tacle.,

T e threaded portion 4.- of the screw shell contact is provided with a plurality oft longitudinally disposed spaced cuts or slits 5 which divide the entire circumference of thescrew threaded portion 4 into a plurality of gripping fingers 6'. These fingers are therefore distributed throughout the entire circumference of the screw shell and provide 'in effect a relatively expansible and cont-ractible screw shell member under the influence of a coiled spring 7 which lies in the valleys of the threads or convolutions of the shell at the outside thereof. l

The spring 7 is, preferably helically wound and the normal 1diameter thereof is less than the normal diameter of the screw shell contact so that when the spring is applied to the outside of the screw shell contact all of the fingers 6 will be pressed inwardly thus providing a relatively constricted yielding threaded sleeve for receiving the lamp plug. The leading thread of the plug however, may be readily fitted into the initial receiving thread of the screw shell Contact and the plug of 100 the lamp screwed into the shell against the frictional gripping action of the multiplicity of gripping elements. Vhen the lamp plug is screwed home, it will be securely and effec- 5 tively gripped throughout its length by the plurality of individual gripping fingers, and thereby efectually prevented from accidental rotation and consequent creeping of the socket.

From the foregoing it will be appa-rent that the primary object of the invention is to provide a screw shell contact having means for uniformly gripping the lamp plug over its entire contacting surface.

Many lamps become darkened due to the plugs creeping out of the screw shell contacts for a sufficient distance to permit the centerplug of the lamp to move out of the centerplug Contact of the receptacle. The present construction however prevents such an occurrence and maintains the lamp illuminated as long as the filament remains unbroken.V

Without further description it is thought that the features and advantages of the invention will be readily apparent to those skilled in the art, and it will of course be understood that changes in the form, proportion and minor details of construction may be resorted to, without departing from the spirit of the invention and scope of the appended claim.

I claim A screw shell contact for electrical receptacles consisting of the screw shell body formed with a spirally threaded portion hav- -ing a plurality of slits disposed longitudinally of the shell body and opening through one end thereof. and a helical spring wire whose convolutions have the same spirality as that ofthe threads ofthe shell body and whose normal diameter is less than the normal diameter of the screw shell body, the convolutions ofthe said spring wire lying in and following the valleys of the shell body threads at the outside thereof.

In testimony whereof I hereunto aix my signature.

EDGAR KENNETH FREEMAN. 

